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Having a very hard time in my PRECALC CLASS

  1. Jan 17, 2013 #1
    Having a very hard time in my PRECALC CLASS.
    When they facto problems they start pulling numbers out of numbers that aren't there..
    Example..

    3(4x+5)^2 (4)(5x+1)^2 + (4x+5)^3 (2) (5x+1)(5)

    Professor said this was the answer.

    a) 2(4x+5)^2(5x+1)[6(5x+1)+5(4x+5)]
    =
    b) 2(4x+5)^2(5x+1)[50x+31] (After combining like terms)

    My questions is

    Where I labeled a) where did she get the 6 from and the 5 from?
    I can see she got the 5 from the original problem, but I thought if she factored out a 2 as a GCF the 5 would be reduced to a smaller number, and the 6 comes out of no where.. HELP
     
  2. jcsd
  3. Jan 17, 2013 #2
    Re: Factoring

    Thanks for the help guys.
     
  4. Jan 17, 2013 #3

    chiro

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    Science Advisor

    Re: Factoring

    Hey DeepSpace9.

    Recall that 3*4 = 12 = 6*2 and 5*2 = 10 = 5*2 [Look at the factorization again carefully with the hint mentioned]
     
  5. Jan 19, 2013 #4
    So the 6 comes from the fact that (3)(4) = 12 and since I factor out a (2) I would need a (6) to = 12 again? I didn't think we could use a 6 since it was not in the original problem.
     
  6. Jan 19, 2013 #5

    chiro

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    Science Advisor

    Yes that's pretty much it.
     
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